1. Technical Field
The present disclosure relates to a semiconductor device.
2. Description of the Related Art
Silicon carbide (SiC) is a semiconductor material that is wider in band gap and higher in hardness than silicon (Si). SiC is applied to power elements such as switching elements and rectifying elements. SiC-based power elements have the advantage, for example, of being better able to reduce electric power loss than Si-based power elements.
Typical SiC-based semiconductor devices are metal-insulator-semiconductor field-effect transistors (MISFETs) and Schottky-barrier diodes (SBDs). A metal-oxide-semiconductor field-effect transistor (MOSFET) is a type of MISFET. Further, a junction-barrier Schottky-barrier diode (JBS) is a type of SBD.
Use of a SiC-MISFET as a switching element, for example, in an electric power converter that controls the drive of a load such as a motor has been under discussion. Use of a MISFET as a switching element in an electric power converter may cause a freewheeling current to flow through the electric power converter when the MISFET is in an off state. In a common inverter circuit, a freewheeling current flows through a freewheeling diode externally connected in antiparallel to the MISFET. In a case where a SiC-MISFET is applied to an inverter circuit, an SBD made of SiC is selected as the freewheeling diode. An SBD is an unipolar element, and has the merit of being smaller in reverse recovery loss than a p-n diode, which is a bipolar element. It should be noted that a SiC-MISFET has inside a parasitic p-n diode including a p-n junction. This parasitic p-n diode is herein referred to as “body diode”. In general, as a freewheeling diode, a body diode is not actively used, but an SBD, which is a unipolar element, is selected.
However, use of separate semiconductor chips to form a transistor and a diode that functions as a reflex diode may lead to an increase in the total number of chips, and accordingly to an increase in footprint. Further, an increase in the number of wirings connecting one chip to another may lead to an increase in parasitic inductance, and by extension to noise generation. Given these circumstances, a configuration in which a transistor and a diode are formed in one semiconductor chip has been proposed. A transistor thus configured is herein referred to as “diode-containing transistor”.
A SiC-based diode-containing transistor is proposed, for example, in International Publication No. 2007/013367. International Publication No. 2007/013367 discloses an example in which a SiC-MISFET includes an arrangement of diode cells each having a Schottky electrode. In this example, an SBD connected in antiparallel to the MISFET can be formed in a chip. This makes it possible to achieve a semiconductor chip that has both the function of switching of the MISFET and the function of the freewheeling diode.